Market sizing: TAM, SAM, SOM explained
Understanding your total addressable, serviceable, and obtainable market is essential for any pitch or business plan.
Why Market Size Matters
Investors and accelerators ask about market size for a simple reason: they want to know if your startup has room to grow into a large business. A great solution to a tiny problem will never return a venture-scale investment. But a mediocre solution in a massive, underserved market can still succeed.
The Three Layers of Market Size
TAM — Total Addressable Market
TAM is the total global demand for your type of product or service, assuming 100% market penetration. It's a theoretical ceiling, not a target.
Example: If you're building invoicing software for small businesses, your TAM is all the spend on invoicing and accounts receivable software globally — potentially $20B+.
How to calculate: Use industry reports, public company filings, or bottom-up estimates (number of potential customers × average spend).
SAM — Serviceable Addressable Market
SAM is the portion of the TAM you can realistically target given your product's focus, geography, and go-to-market approach.
Example: If you're focused on the MENA region and on freelancers specifically, your SAM might be $300M.
How to calculate: Narrow the TAM by segment, geography, and channel constraints.
SOM — Serviceable Obtainable Market
SOM is what you can realistically capture in the near term (3–5 years), given your resources and competitive position. This is the number you should be able to defend with a bottoms-up model.
Example: If you plan to capture 5% of MENA freelancers in 3 years, your SOM might be $15M in ARR.
How to calculate: Build a model: channels × conversion rates × average revenue per customer.
Bottom-Up vs. Top-Down
Top-down: Start with industry reports, then slice downward. Fast but imprecise.
Bottom-up: Start with the unit economics and customer count, then multiply up. Slower but far more credible.
Investors much prefer bottom-up models because they reveal whether you understand your customer and sales motion.
Common Mistakes
- Citing a huge TAM without explaining why the SAM is meaningful
- Using a SAM that's too optimistic (e.g., assuming instant global reach)
- Not being able to explain the math behind any number you claim
- Confusing revenue market size with number of users or transactions
The Right Mindset
Market sizing isn't just for investors — it's a discipline that forces you to understand the true scale of your opportunity and the constraints of your go-to-market. Build models you believe in, and you'll present them with conviction.